Recently attention has been given to so-called ground fault circuit interrupter (GFCI) circuits which are designed automatically to open electrical circuits upon the existence of shock hazards. These GFCI's detect leakage currents, that is, imbalances in the current flowing through the power supply conductors. Certain known GFCI's malfunction if supply conductors are transposed. Accordingly, a secondary object of this invention is to eliminate the chance of malfunctioning of such GFCI's.